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|
;
; Macros to disable and enable the ROM on Atari XL systems.
;
; Christian Groessler, chris@groessler.org, 19-Sep-2013
;
;
; Defines which modify the operation of the macros:
;
; CHARGEN_RELOC: If defined, CHBAS and CHBASE are updated when
; enabling or disabling the ROM.
; If the ROM is enabled, $E0 is written to CHBAS
; and CHBASE.
; If the ROM is disabled, the upper byte of
; __CHARGEN_START__ is written to CHBAS and CHBASE.
; USEWSYNC: If defined, the code waits for horizontal retrace
; before switching the ROM and updating CHBAS and
; CHBASE. This define only has effect if CHARGEN_RELOC
; is also defined.
.ifdef __ATARIXL__
.ifdef CHARGEN_RELOC
.macro set_chbase val
lda #val
sta CHBAS
sta CHBASE
.endmacro
.else ; above CHARGEN_RELOC, below not
.macro set_chbase val
.endmacro
.endif ; .ifdef CHARGEN_RELOC
.if .defined(USEWSYNC) .and .defined(CHARGEN_RELOC)
.macro wsync
sta WSYNC
.endmacro
.else ; above USEWSYNC, below not
.macro wsync
.endmacro
.endif
; "disable ROM" macros
.macro disable_rom
lda PORTB
and #$fe
wsync
sta PORTB
set_chbase >__CHARGEN_START__
.endmacro
.macro disable_rom_quick
lda PORTB
and #$fe
sta PORTB
set_chbase >__CHARGEN_START__
.endmacro
.macro disable_rom_val val
lda val
wsync
sta PORTB
set_chbase >__CHARGEN_START__
.endmacro
; "enable ROM" macros
.macro enable_rom
lda PORTB
ora #1
wsync
sta PORTB
set_chbase $E0
.endmacro
.macro enable_rom_quick
lda PORTB
ora #1
sta PORTB
set_chbase $E0
.endmacro
.else ; above __ATARIXL__, below not
.macro disable_rom
.endmacro
.macro enable_rom
.endmacro
.endif
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